1. Field of the Invention
This invention relates to an image forming apparatus having a sheet processing apparatus for fetching sequentially sheets on which images are formed by an image forming means, stapling the plural sheets with a stapling means, and folding the sheets in folio.
2. Description of Related Art
Some image forming apparatus such as photocopiers or the like today can do bookbinding by stapling plural sheets and folding the sheets in folio where connected with a sheet processing apparatus. Such an apparatus forms images on double sides or the sheets at an image forming apparatus body, fetches sequentially the sheets, staples the sheets at about the center of the sheet bundle upon driving the stapler unit, and folds the sheets in folio where the sheets are conveyed to a folding means.
As a structure for folding the sheets in folio, it is structured by a folding roller means made of a roller pair, and a projecting means made of a projecting plate and so on. The projecting plate folds the sheet bundle upon projecting the stapled position of the sheet bundle between the nip portions, and the folded sheet bundle is pressed and conveyed by the roller pair to fold the bundle in folio. Therefore, the sheet bundles delivered to the delivery tray are delivered in a state that the sheet bundles are folded in folio and bound in a book form at the center stapled position of the sheets.
Where the sheet processing apparatus performs a folding operation, if the frictional coefficient between sheets is low, the sheets may slip when the sheet bundle folded in folio is pulled by a folding roller, thereby possibly generating tears at the stapling positions. Such tears tend to occur right after the start of the folding operation. At that time, if images are formed at the folding start positions and toners cling to there, the sheets located inside in a fold form when the folding roller pulls inside the sheets are easily returned, thereby causing tears easily.
This invention is made with respect to the above viewpoint and it is an object to provide an image forming apparatus capable of bookbinding sheet bundles without generating tears when the sheet bundles are pulled inside.